The aim of this clinical trial is to investigate the advantages of single-operator laser-assisted ultrasound-guidance comparing with traditional ultrasound guidance in peripheral venous catheterization.The primary question addressed is whether single-operator laser-assisted ultrasound-guidance could improve the first-attempt success rate of peripheral venous catheterization compared with traditional ultrasound guidance.

One hundred patients receiving cardiac surgery were randomized into two groups control group (group T, 50 patients), and experimental group (group L, 50 patients). In group T, ultrasound-guided short-axis out-of-plane technique with dynamic needle tip positioning is employed. The operator holds the puncture needle in the right hand at an angle of approximately 30-40° to the skin, and inserts the needle along the projection path of the laser on the body surface at a distance of about 0.5 cm from the probe. Under direct visualization, the needle tip is inserted into the blood vessel, and then the probe is slowly moved along the course of the vein to keep the needle tip directly above the vessel, thereby obtaining the optimal axial cross-section with this as the axis. After observing the high-echo needle tip displayed in the blood vessel on the ultrasound image, keep the puncture needle still and move the ultrasound probe until it disappears. Slowly advance the puncture needle so that the needle tip is always located in the center of the blood vessel during the puncture process. After observing the needle body reaching the blood vessel, withdraw the needle core, and then insert the catheter into it. In group L, an nurse prepares the equipment as follows before the patient enters the operating room: the mechanical arm is fixed near the operating table, and the laser emitter is attached is attached nearby. The tightness is adjusted to ensure a tighter fit between the probe and its housing. The ultrasound probe is then placed over the middle of the elbow and slightly moved so that the central auxiliary line on the screen passes through the center of the blood vessel. After the image is saved, another nurse measures the diameter and depth of the vein. The first point under the middle of the ultrasound probe is marked with a sterile marker pen. The probe is then moved 1.0 cm proximally, and the second point is marked in the same way. The probe is fixed to the skin at an angle of approximately 75°. After turning on the laser, the laser beam is aligned to pass through the middle mark of the ultrasound probe (centered on the vein lumen) and the two marked points: the laser beam thus becomes the skin projection of the venous anatomical path. At this point, the probe is fixed with the mechanical arm, and the needle is held in the right hand. Finally, the height of the ultrasound screen is adjusted to be level with the operator's eyes to reduce head and neck movement and facilitate guidance. Then, venous catheterization was completed with the "dynamic needle tip positioning" method.

Inclusion Criteria:

1. aged 18-80 years
2. BMI 18-30 kg/m²
3. ASA classification 1-4

Exclusion Criteria:

1. infection or hematoma at the puncture site
2. patients mentally unstable or unable to cooperate
3. patient refused to participate